Zanuttini D., Lestuzzi C., Nicolosi G.L., Dall’Aglio V., Pavan D., Sparacino L.
Hospital Civil - Pordenone (Italy) Division of Cardiology
Several right ventricular pathologies have been related to ventricular arrhythmias (VA) with left bundle branch block. (LBBB) pattern, including sequelae of cardiac surgery, ischemic heart disease, right ventricular cardiomyopathies, Ebstein’s anomaly etc. (1-6). The correlation between morpho-functional abnormalities, electrocardiographic. Holter or electrophysiological findings and clinical outcome, however, are still under debate in most cases. Moreover, arrhythmias originating from the right ventricle (RV) have been observed also in subjects without clinically overt heart disease (7). On the other hand, it is well recognized that some RV pathologies, whose first sign is often a VA with LBBB pattern, and that show important morphological abnormalities, may lead to life-threatening arrhythmias and sudden death, especially in young people (7-13). The importance of differential diagnosis between those pathologies -mostly right ventricular arrhythmogenic disease (RVAD), and right ventricular dilated cardiomyopathy (RVDC)- and other RV abnormalities is then clear from a clinical point of view, even if there are several problems in trying to correlate electric phenomena with morphofunctional abnormalities:
1) A LBBB pattern of VA is not pathognomonic of right ventricular origin of the arrhythmia since also VA arising from the interventricular septum may show that pattern. This is mostly frequent in coronary heart disease. 2) The complex shape of the right ventricle make it difficult to standardize the imaging approach. This shape may also be influenced by thoracic cage abnormalities as well by hemodynamic conditions. 3) A wide variability of echocardiographic and angiographic RV aspects have been described in subjects without any known RV pathology. The so-called "normal right ventricle" is then still a non-well defined entity (14,15).
We will then try to examine in details the most important pathological, physiological or paraphysiological conditions that can be related to RV morphology abnormalities and their relationships with VA.
A) Arrhythmogenic right ventricular disease (ARVD) (also called "RV dysplasia, "RV cardiomyopathy", "arrhythmogenic RV dysplasia" and so on). It is characterized by a fibro-fatty degeneration of the RV wall. From a macroscopic point of view, the right ventricle shows thinning of the free wall; global or segmental dilatation, sometimes with bulging areas, hypertrophy or degeneration of the moderator band, hypertrophy of the trabeculae; left ventricular abnormalities or dysfunction may be associated (8,10,16-18). Several echocardiographic and angiographic findings have been reported as diagnostic markers of the disease, although a gold standard for the diagnosis has not yet been established (19-25). VA could be originated both from late potentials and from reentry mechanisms (26-28). A good correlation was found by some Authors
between the site of segmental morphofunctional abnormalities and origin of the VA, but other Authors failed to confirm these data (7-9,29-31). The problem is even more complex, since the disease can be evolutive: it has been suggested that both VA may appear several years before any evident morphofunctional abnormality, and asymptomatic patients with echo-angiographic RV alterations may develop clinically evident VA only at a later time (30,32-34). Also the correlation between the echocardiographic and/or angiographic findings and the severity of arrhythmias or the clinical outcome are not well defined (9,11-13,16,26). In a previous study we failed to find any correlation between single morphofunctional abnormalities and severity of arrhythmias, although we observed more severe arrhythmias in the patients with more widespread RV abnormalities; other Authors did not find any significant correlation between the extent of RV involvement and the severity of the arrhythmias (35). The presence of late potentials seems to be independent from the extent of the R.V involvement (36). The clinical outcome is widely variable, with symptoms ranging from palpitations to syncope and sudden death. VA may be controlled by antiarrhythmic drugs and surgery, but can also spontaneously disappear (37-40). It should be kept in mind, however, that the conduction system can also be involved, and in the case of a syncope or sudden death the possibility of a hypokinetic arrhythmia should also be considered (41,42).
B) Right ventricular dilated cardiomyopathy. (RVDC) It is characterized by fibrous degeneration of the RV wall, without fatty infiltration, sometimes with inflammatory phenomena; it may or not be associated with a left ventricular dilated cardiomyopathy. At echocardiography and angiography, the right ventricle appears to be globally dilated, with diffuse hypokinesia (9,43,44). From a clinical point of view, it may be characterized by VA (even ventricular tachycardia and fibrillation) or by congestive heart failure. The only possibility of differential diagnosis with other RV cardiomyopathies could be myocardial biopsy, but also this technique can fail in some cases
C) Uhl’s anomaly. This very rare condition, characterized by an extremely thin right ventricular wall, without muscular tissue, is relevant mostly because it should be differentiated from RVAD. Some Authors suggested that the two conditions are only different aspects of the same disease (16,17,25,45). Major VA have been reported also in Uhl’s anomaly. Differentiation from RVDC could also be very difficult.
D) Thoracic cage and lung abnormalities. Because of its structure and shape, the right ventricle is easily distorted by ab extrinseco compression, and by hemodynamic acute or chronic changes (46,47). The straight back syndrome and pectus excavatum (PE) can affect RV morphology. We prospectively studied by radiology, echocardiography, Hotter and stress test 29 patients (pts) (24 males, 5 females) with PE comparing them with 20 normal subjects (15 males, 5 females). One or more RV morphofunctional abnormalities were observed in 21/29 pts with PE, and only in 4/20 normal controls. The more frequent abnormalities (p<0.05) were: apical bulging (14 vs 3), global dilatation (8 vs 0), hypertrophic trabeculae (7 vs 0). Also mitral valve prolapse was more frequent in the PE group than in the control group (14/29 vs 2/20, p<0.05). Diastolic RV area in apical 4-chambers view was 17.47±3.5 scm in PE versus 15.1±6.9 cm2 in normals (p<0.02),: RV outflow tract diameter was 2.4±0.54 cm2 in PE versus 2.97±0.54 in normals (p<0.001). Arrhythmias were more frequent in PE than in the control group (25/29 versus 5/20, p<0.001): premature ventricular contractions (PVC) were present in 7/29 PE pts versus 0/20 normal controls, but ventricular tachycardia was never observed and complaints of major symptoms related to the arrhythmia were never reported in either group. Only one pt with PVC at Holter had a normal right ventricle at echocardiography (he had mitral and tricuspid valve prolapse): the others had one to four different RV abnormalities-Even chronic lung disease may lead to RV morphological abnormalities which can be detected at echocardiography (48). In this particular pathology, however, arrhythmias seem to be related mostly to blood gas and acid-base imbalance, and no particular correlation with RV morphological abnormalities has been reported so far to our knowledge.
E) "Athlete’s heart". Intensive regular physical training, as in competitive athletes, leads to several morphological and functional cardiac changes. There are some differences between the changes induced by prevalent isotonic or isometric exercise, while no significant differences were observed between elite and high level athletes, if constantly trained. The right ventricle is usually globally dilated, and its ejection fraction at rest may be slightly decreased (49). Most of the studies, however, have been focused on the left ventricular structural and functional changes, and only a few data on the right ventricle are available in Literature. We studied by two-dimensional echocardiography 85 high level, well trained athletes (60 males, 17 females aged 12 to 45 years: 52 of them were performing dynamic sports, 14 isometric and 18 mixed effort sports) and 28 normal subjects (controls). The diastolic and systolic RV area from the apical 4-chambers view, corrected for the body surface area, were 9.66±2.2 cm2 and 4.42±1.3 cm2 in athletes versus 7.4U2.3 and 3.12±1.3 cm2 in controls (p<0.001). Also the maximal longitudinal and transverse RV diameter were increased in athletes as compared to controls (p<0.01). The RV ventricular area fractional reduction was slightly decreased in athletes (31.3±7.8 versus 35-5±6.9,p<0.05). Accordingly to other reports, RV findings remained within the normal range, and significant VA were not observed. Actually, in most cases described in Literature regarding athletes who had major VA or who died suddenly, a structural heart disease was found, more often coronary heart disease and right ventricular arrhythmogenic disease (50,51).
CONCLUSIONS: Several pathological and paraphysiological conditions may affect the right ventricle from the morphological and functional point of view, but only some of them are related to VA. Severe VA are usually associated with intrinsic structural abnormalities of the right ventricle, rather than to simple distortion of the RV wall. In ARVD the correlation between morphological abnormalities and VA is probably due to a common cause -i.e. the degenerative process- even though in the individual case the correlation can not always be confirmed. In subjects with RV morphological abnormalities and VA, an electro-physiological study seems to be, at present, the most reliable indicator of underlying RV disease and of the prognosis, even though the clinical outcome may to be influenced by several other factors.
ABSTRAC: The possible relationship between R.V abnormalities and VA in different conditions is discussed. RV morphological abnormalities are frequent in some pathological and physiological or paraphysiological conditions, and may be related to simple VA. Nevertheless, major VA (life-threatening or symptomatic) are usually observed only in patients with underlying structural heart disease (mostly cardiomyopathies and coronary pathology).
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Key words: Right ventricle, ventricular arrhythmias.